This invention relates generally to motors and stationary assemblies therefor and, particularly, to an improved stationary assembly for providing positive torque parking positions in a single phase electronically commutated motor for use in a horizontal axis washing machine.
In general, a motor such as an electronically commutated or brushless motor has permanent magnets mounted on its rotor. The stator of such a motor has a plurality of teeth and wire-wound coils on the teeth which, when energized with current, interact with the permanent magnet rotor to produce positive or negative torque, depending on the direction of the current with respect to the polarity of the magnets. The polarity of the magnets relative to the stator winding alternates when the rotor moves unidirectionally. Thus, it is necessary to alternate the direction of the stator current in synchronism to maintain a constant direction of torque. An electronic inverter bridge typically controls energization of the stator winding for controlling the direction and amount of torque produced by the motor as well as the rotor shaft speed.
As is known in the art, single phase brushless motors typically have starting problems. The magnetic saliencies formed by the stator teeth cause a cogging torque which forces the permanent magnet rotor to rest, or park, at particular angular positions in the absence of external electrical or mechanical stimulus. This cogging torque is also referred to as an indenting or parking torque. In a single phase motor, the rotor""s parking positions can coincide with positions of zero electromagnetic torque production which makes it difficult to start the motor. This problem can also make it more difficult to reverse the rotor""s direction of rotation.
One approach to overcome this problem is to provide a starting winding which disadvantageously increases the cost and complexity of the motor.
Another approach is to provide parking cuts in the stator teeth or to provide additional parking magnets or parking laminations. Although several motor configurations are known for parking a motor""s rotor in a particular position, these motor configurations increase the cost of the motor and/or fail to provide parking positions with sufficient starting torque, especially for low torque motors such as single phase electronically commutated motors.
In general, brushless DC motors are disclosed in, for example, U.S. Pat. Nos. 5,423,192, 4,933,584 and 4,757,241, all of which are commonly assigned with the present invention described herein and the entire disclosures of which are incorporated herein by reference. In particular, single phase motors are disclosed in, for example, U.S. Pat. Nos. 5,483,139, 5,465,019, 5,140,243, 4,724,678, 4,635,349, 4,626,755, 4,313,076 and 3,134,385, all of which are commonly assigned with the present invention described herein and the entire disclosures of which are incorporated herein by reference.
Among the several objects of this invention may be noted the provision of an improved motor which provides a positive torque parking position; the provision of such a motor which is particularly well suited for use in a horizontal axis washing machine; and the provision of such a motor system which is economically feasible and commercially practical.
Briefly described, a motor embodying aspects of the present invention includes a rotor which is rotatable about an axis of rotation and a stator in magnetic coupling relation with the rotor. The stator includes a plurality of teeth each having a radially extending shaft and an axially extending face. The faces of the stator teeth define an aperture for receiving the rotor and the faces of the stator teeth and the rotor define an air gap therebetween. Each stator tooth also has a notch in its face that is approximately at least as wide as the shaft of the stator tooth so that the stator has a magnetic configuration relative to the rotor for parking the rotor in a rest position corresponding to a positive torque starting position. The motor also includes a winding on the shafts of the stator teeth and a control circuit for controlling current in the winding whereby an electromagnetic field is produced for rotating the rotor at a desired speed or torque during operation of the motor.
In another embodiment, the invention is directed a stationary assembly for a motor having a rotor which is rotatable about an axis of rotation and which is in magnetic coupling relation with the stationary assembly. The stationary assembly includes a stator core that has a plurality of teeth each having a radially extending shaft and an axially extending face. The faces of the teeth define an aperture for receiving the rotor and the faces of the teeth and the rotor define an air gap therebetween. Each tooth also has a notch in its face that is approximately at least as wide as the shaft of the tooth so that the stator core has a magnetic configuration relative to the rotor for parking the rotor in a rest position corresponding to a positive torque starting position. The stationary assembly also includes a winding on the shafts of the teeth that is adapted to be energized for producing an electromagnetic field to rotate the rotor at a desired speed or torque during operation of the motor.
Other objects and features will be in part apparent and in part pointed out hereinafter.